My experience was a bit different than that, not sure what the population was at the time, but it is medium now. My first raiding guild started raiding in a guild alliance and some PuGs, we then recruited more and absorbed the raiders in our alliance and ran under one banner. We slowly cleared all of the content until Twin Emps in AQ40 and did the easy Naxx bosses until the pre-expansion lull hit. We certainly weren’t the best, but you didn’t need the best players to do 40-mans until late Vanilla. We were right in the middle in terms of our server progression on Alliance side, with 2 guilds better than us, 1-2 guilds on par and 2-3 guilds lower.